Semiconductor sensor chip and method for producing the chip, and semiconductor sensor and package for assembling the sensor

ABSTRACT

The present invention is a method of making an acceleration sensor chip. The sensor chip is prepared from a SOI wafer having a silicon substrate, a SiO 2  layer and a silicon thin film. A dopant is ion implanted at a position corresponding to a semiconductor strain gauge on the silicon thin film to form a diffusion resistor, and for forming devices necessary for circuit construction on said silicon thin film. A protective film is provided on the entire surface of the wafer, and a plurality of through holes penetrating the silicon thin film are formed by patterning and etching to make a weight part and a beam part connected to a support frame part on the periphery. The SiO 2  layer under the weight part and the beam part is removed by wet etching to form the through holes, while leaving the protective film in place. The protective film is removed and a resist coated over the entire surface of the wafer. A slit for dividing the chip is formed part way through the wafer by dicing. The resist is removed by ashing with an O 2  plasma and the chip is divided by concentrating a stress on the slit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is divisional of application Ser. No. 09/241,096, filed Feb. 1,1999 which is a continuation-in-part of abandoned application Ser. No.09/160,189 filed on Sep. 25, 1998 which is a continuation-in-part ofabandoned application Ser. No. 09/061,876 filed Apr. 17, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor sensor chip used in awide range of applications such as automobile, aircraft, medicalservice, measurement, and calibration, and to a production method formanufacturing the sensor chip. It also relates to a semiconductor sensorcomprising the semiconductor sensor chip, and to a package forassembling the semiconductor sensor.

2. Description of the Related Art

An example of a conventional acceleration sensor chip disclosed inJapanese Patent No. 2551625 is shown in FIG. 1A and FIG. 1B. FIG. 1A isa perspective diagram, and FIG. 1B is a sectional diagram taken alongline IB—IB of FIG. 1A. In this semiconductor acceleration sensor chip, asilicon single crystal is etched to form a support frame 1, weight parts2 a and 2 b, a beam part 3 a for connecting the weight part 2 a and theweight part 2 b, and beam parts 3 b and 3 c for connecting the weightpart 2 a, the weight part 2 b and the support frame with each other.Gauge resistors 4 a, 4 b, 4 c, and 4 d are provided on the beam parts 3a, 3 b, and 3 c, and a Wheatstone bridge is formed of these gaugeresistors. When an acceleration is exerted in a direction shown by thearrow in FIG. 1B, resistances of the gauge resistors are changed. Theacceleration sensor chip measures the acceleration utilizing changes ofthe resistances.

In general, in the semiconductor acceleration sensor chip of this kind,a silicon substrate is deeply etched from the backside to formthick-walled weight parts of about 300 μm to 400 μm and thin-walled beamparts of about 10 μm to 50 μm. As the silicon substrate, a 4 inch waferis often used. The reason for this is as follows:

Because the substrate is required to be deeply etched to form a thinbeam part, a small wafer thickness is advantageous in terms ofproductivity due to the limitation of processing time. A wafer sizewhich can be handled in the process with a thickness of about 300 μm to400 μm, corresponding to the thickness of the beam part, is about 4inches, and a larger wafer of 5 or 6 inches is substantially difficultto handle. Further, as shown in FIG. 1B, a wafer before dicing is formedwith a number of thin-walled, low resonance frequency beam parts and islow in rigidity. A shock applied during dicing tends to generate aresonance phenomenon of the sensor part or the wafer itself, and thereis a danger of an excessive displacement or stress applied to the beamparts. Consequently, the wafer size is limited because of this handling.

In the case of the above-described semiconductor acceleration sensorchip, a greater part of the cost is determined by chip size and wafersize. When acceleration sensor chips are produced with the sametechnical level, if the wafer size is large, a large number of chips canbe processed in a single batch process, and the unit price of the chipis naturally reduced. However, in the above-described prior art, usablewafer size is limited, and cost reduction can only be achieved byreduction of the chip size. However, the chip size reduction is limitedas it may reduce production yield. Further, in the future, with thetrend to larger diameter semiconductor wafers, a decrease in supply of4-inch wafers is anticipated. If such an acceleration sensor chip isachieved with larger-diameter wafers of 5 inches, 6 inches or the like,a beam part of 10 μm to 30 μm in thickness must be formed from a siliconsubstrate of about 600 μm to 700 μm in thickness, which not onlyincreases the etching time but also leads to a reduced production yield.

Another example of a prior art acceleration sensor chip is one which isdisclosed in Japanese Laid-Open Patent Application No. 8-248058.

The second prior art example will be described with reference to FIGS.2A and 2B. FIG. 2A is a perspective diagram of the acceleration sensorchip. FIG. 2B is a schematic diagram showing the structure of a combelectrode unit as part of the acceleration sensor chip.

This acceleration sensor chip has a three-layered structure comprising afirst layer (support plate) 10, a second layer 11 as an insulation layeron the first layer, and a third layer 12 coated thereon. For example, itcomprises a SOI (silicon-on-insulator) or epitaxial polysilicon wafer(polysilicon as a third layer grown on a single crystal siliconsubstrate through an insulation layer).

The third layer 12 is provided with a displaceable first support body 13separated from the first layer 10 and a non-displaceable second supportbody 16 which is connected with the first layer 10. The first supportbody 13 has a mass body 15 disposed at the center and a plurality offirst plates 14 extending in a direction perpendicular to the mass body15. The second support body 16 has two mounting parts 18 straightlydisposed at both ends and a plurality of second plates 17 extending in adirection perpendicular to the mounting parts 18. The second layers 11disposed at lower parts of the plurality of first plates 14 and the massbody 15 are removed by etching so that the first support body 13 isdisplaceable in parallel with respect to the surface of the first layer10.

Further, the plurality of first plates 14 and the plurality of secondplates 17 respectively form comb electrodes, which, when thedisplaceable mass body displaces in a direction perpendicular to thefirst plate 14, measure an acceleration by utilizing a change incapacitance between the first plate 14 and the second plate 17. Stillfurther, a conductor 19 for conducting these comb electrodes to anexternal circuit is electrically insulated from the first layer 10 bythe second layer (insulation layer) 11, and further electricallyinsulated from the third layer 12 by a cutout 20.

In the capacitive type acceleration sensor chip using comb electrodes ofthis type, in order to increase the change in capacitance to affect anincrease in sensitivity, it is necessary to form a structure with adecreased rigidity of a movable electrode (first plate 14). There aretwo factors that cause variations in sensitivity when such a sensor isconstructed. A first factor is a variation in rigidity of the movableelectrode (first plate 14) that is dependent on the productionprecision, and where the sensitivity is small when the rigidity is high.A second factor is the variation of gap between the movable electrode(first plate 14) and a fixed electrode (second plate 17), where thesensitivity decreases as the gap increases.

With respect to the first sensitivity variation factor, in general,production methods such as wet etching, RIE (Reactive Ion Etching),plasma etching and the like are used in process for producing the gapbetween the movable electrode and the fixed electrode and in the processof producing the support part of the movable electrode. With theseproduction methods, since etching speed in a depth direction variesdepending on the processing width, a variation occurs in the processingshape depending on the width of etching pattern. To prevent this, it isnecessary to make a complex mask design in consideration of the etchingspeed which varies for every pattern width, resulting in a complicatedprocess.

The second sensitivity variation factor will now be described in detail.In a sensor chip using a wafer in which polysilicon is formed as a thirdlayer through an insulation layer on a single crystal silicon substrateor a SOI wafer, the second layer comprising an insulation layer, such asSiO₂, between the first layer and the third layer and a passivation filmfor protecting circuits on an upper surface of the third layer areformed. As a result, there is a loss of balance in the internal stressbetween a surface on the side where the second and third layers aredisposed on the first layer which controls the rigidity of wafer, andthe opposite back surface, resulting in a warped wafer. Therefore, thereis a problem in that due to such a warping of wafer, a strain occurs inthe sensor structure formed on the third layer, thereby, there isvariation in the gap between the movable electrode and the fixedelectrode constituting the comb electrodes, for example, of thecapacitive type sensor chip. Yet further, there is another problem inthat in an initial state before measurement when such a detectedphysical amount is not yet generated, generation of a strain results inan increase in offset, which requires a complicated correction circuit.

Further, in the acceleration sensor chip, after the insulation layer isetched to form a number of sensor chips, in a subsequent process such asa dicing process to divide it into discrete chips, there is a problem inthat foreign matter may enter the gaps between the comb electrodes.Also, static electricity generated during sensor operation may attractforeign matter from other packaged parts to the sensor part. Dependingon the size of entering foreign matter, operation of the comb electrodesmay be disturbed. Even when the size of the entering foreign matter issmall enough that the matter does not disturb the operation of the combelectrodes, depending on the characteristics of the entering foreignmatter, capacitance between the comb electrodes may be varied. Stillfurther, there is another problem in that, when an epitaxial polysiliconwafer is used, since polysilicon is produced by a film forming apparatussuch as a CVD apparatus, even if the same in outer dimensions, adeviation occurs in mechanical characteristics such as internal stressor breakdown stress, resulting in degraded reliability of the sensorchip.

The sensor chip is incorporated in a package 60, forming a semiconductorsensor. FIG. 3 shows an example of a prior art semiconductor sensor. Inthis prior art example, an acceleration sensor chip 50, for detecting anacceleration in a direction 70 perpendicular to the chip surface, ismounted on a printed circuit board 80 so that the perpendiculardirection of the chip surface is correctly in line with the direction 70of the acceleration. More specifically, a package 60 incorporating theacceleration sensor chip 50 is fixed with a sensor retaining pin 91 to ahigh-rigidity substrate 90, and the high-rigidity substrate 90 ismounted on the printed circuit board. Package terminals 61, electricallyconnected with input/output terminals (not shown) of the accelerationsensor chip, are connected to terminals 81 of the printed circuit withwiring 82. A similar construction to the semiconductor accelerationsensor shown in FIG. 3 is described in Japanese Patent ApplicationLaid-open No. 8-94663 (1996) (U.S. patent application Ser. No.08/189,948).

The sensor chip illustrated in FIG. 1A and FIG. 1B, for example, is usedas the acceleration sensor chip 50. As for the semiconductor sensorillustrated in FIG. 3, it is possible to obtain an output according tothe acceleration generated in the direction 70 perpendicular to thesurface of the acceleration sensor chip 50.

However, the above-described prior art acceleration sensor has thefollowing problems:

Because the acceleration sensor package 60 is mounted on the printedcircuit board 80 through the high-rigidity substrate 90, the arearequired for mounting is increased, and the entire accelerationmeasuring system, including the printed circuit board 80, is increasedin size.

Mechanical vibration of the wiring 82 transmits vibration to the sensorpackage, resulting in mechanical noise. Further, since the wiring 82 islocated in a three-dimensional space, it tends to cause an inductionnoise from outside the sensor chip.

A process for fixing the package 60 to the high-rigidity substrate 90, aprocess for wiring from the package 60 to the printed circuit board 80and the like are required. These processes are difficult to automate,resulting in increased assembly cost.

SUMMARY OF THE INVENTION

A first object of the present invention is to solve the above-describedproblems in prior art conventional semiconductor sensor chips.

Specifically, a first object of the present invention is to solve thefollowing problems:

(i) in an acceleration sensor chip using a simple piece of singlecrystal silicon wafer, use of a thick, large-diameter wafer isdifficult,

(ii) in a capacitive type acceleration sensor chip using SOI wafer orepitaxial polysilicon wafer,

a) increasing the sensor sensitivity is difficult,

b) in the dicing process after removing the insulation layer, foreignmatter may enter the sensor structure,

c) variations of sensitivity and offset are large because of the strainof sensor caused by the warping of wafer.

d) detection capacity is changed by foreign matter, and

e) the sensor structure possesses less reliable mechanicalcharacteristics.

A second object of the present invention is to provide a semiconductorsensor and a semiconductor sensor package which solves the problems ofconventional semiconductor sensors mentioned above by reducing themounting area, preventing generation of mechanical and induction noisesdue to wiring, and lowering the mounting cost.

To achieve the first object, in accordance with one aspect of theinvention, there is provided an acceleration sensor chip comprising asupport frame part, and a sensor structure including at least onedisplaceable weight part, and a beam part for connecting the weight partto the support part. The support frame part and the sensor structure areformed on a silicon substrate through an insulation layer, wherein theinsulation layer between the sensor structure and the silicon substrateis removed. The beam part comprises a plurality of sets of beams whichare parallel to each other, the weight part is connected to the supportframe part by the plurality of sets of parallel beams, and at least twosemiconductor strain gauges are formed on the surface of at least oneset of the plurality of sets of parallel beams.

In this case, there is preferably one weight part, the plurality of setsof parallel beams are protrudingly formed to four corner parts of theweight part, and four semiconductor gauges are respectively formed onthe surfaces of the plurality of sets of beams, thus forming aWheatstone bridge. In an alternative case, there are preferably twoweight parts, the plurality of sets of parallel beams are formed betweenthe two weight parts and the support frame part and between the twoweight parts, at least one semiconductor strain gauge is formed on therespective surface of (a) at least one of beams (b) between one of thetwo weight parts and the support frame part of the plurality of sets ofparallel beams, at least one of beams between the other of the twoweight parts and the support frame part, and (c) a beam between the twoweight parts, and a Wheatstone bridge is formed of the semiconductorstrain gauges.

Further, preferably, the thickness of the beam part is smaller than thatof the weight part.

Still further, in the acceleration sensor chip according to the presentinvention, a sensor structure comprises a displaceable weight parthaving a magnetic thin film formed on the surface and a beam part forconnecting the weight part to the support frame part, the sensorstructure being formed on a silicon substrate through an insulationlayer, the insulation layer between the sensor structure and the siliconsubstrate removed, and, on the support frame part on the periphery ofthe weight part, a coil is formed to surround the weight part.

Further, according to another aspect, there is provided an accelerationsensor chip comprising a support frame part, and a plurality of sensorstructures including displaceable weight parts respectively havingmagnetic films formed on the surfaces, and beam parts for connecting theweight parts to the support frame part, the support frame part and thesensor structures being formed on a silicon substrate through aninsulation layer, wherein the insulation layer between the plurality ofsensor structures and the silicon substrate is removed, coils arerespectively formed surrounding the weight parts on the support framepart on the periphery of the respective weight parts, and the pluralityof coils are connected in series.

Here, it is preferable that a plurality of sensor groups comprising therespective plurality of sensor structures and the plurality of detectioncoils connected in series, the sensor groups differing in numbers of thesensor structures, and the detection coils are formed on a samesemiconductor chip.

In the above-described acceleration sensor chip, it is desirable tofurther provide a means for performing a self diagnosis, and anamplifier circuit and a digital adjustment circuit are formed on thesemiconductor chip on which the acceleration sensor chip is formed.

According to a yet further aspect, there is provided an angularacceleration sensor chip comprising a first sensor group including afirst support frame part, and a plurality of first sensor structurescomprising displaceable first weight parts having magnetic thin filmsformed on the respective surfaces and first beam parts for connectingthe first weight parts to the first support part, the first supportframe part and the first sensor structures being formed on a siliconsubstrate through an insulation layer, wherein the insulation layerbetween the plurality of first sensor structures and the siliconsubstrate is removed, first detection coils are respectively formedsurrounding the first weight parts on the first support frame part onthe respective periphery of the first weight parts, and the plurality offirst detection coils are connected in series;

a second sensor group including a second support frame part, and aplurality of second sensor structures comprising displaceable secondweight parts having magnetic thin films formed on their respectivesurfaces and second beam parts for connecting the second weight parts tothe second support frame part, the second support frame part and thesecond sensor structures being formed on the silicon substrate throughan insulating layer, wherein the insulating layer between the pluralityof sensor structures and the silicon substrate is removed, seconddetection coils are respectively formed surrounding the second weightparts on the second support part on the respective periphery of thesecond parts, and the plurality of second detection coils are connectedin series, the first and second sensor groups being formed on a samesemiconductor chip;

the first sensor group and the second sensor group are equal in numberof sensor structures, and the first sensor group and the second sensorgroup are disposed symmetrically about a detection axis as an axis ofsymmetry,

the first and second detection coils of the first and second sensorgroups form closed loops so that currents flowing through the pluralityof first and second detection coils of the first and second sensorgroups flow in the same direction when an angular acceleration generatesabout the detection axis. This embodiment may further comprise means foramplifying signals from the plurality of first and second detectioncoils and means for integrating outputs from the plurality of detectioncoils to output an angular acceleration signal.

According to a yet further aspect, there is provided an accelerationsensor chip characterized in that a third layer is formed on a firstlayer of a support substrate through an insulating second layer, thethird layer has a sensor structure, and the second layer between adetection surface of the sensor structure and the first layer isremoved, and, a beam part having a detection device, and a weight parthaving a plurality of cutouts of a same width formed over the entiresurface are provided on the detection surface of the sensor structurewith the second layer removed.

Here, it is preferable that a film of a material having a smallerthermal expansion coefficient than the material of the first layer beformed on the backside of the first layer.

Further, it is desirable that the same width of the plurality of cutoutsformed on the sensor structure be a width of 2 μm or less.

Still further, as a substrate comprising the first layer, the secondlayer and the third layer, a silicon-on-insulator substrate may be used,or a substrate having polysilicon formed as the third layer on a singlecrystal silicon substrate through an insulation layer be used.

According to a yet further aspect, there is provided a production methodof an acceleration sensor chip of the following processes.

Specifically, the production method of the acceleration sensor chip ischaracterized by comprising:

(a) a step for preparing a SOI wafer comprising a silicon substrate, aSiO₂ layer and a silicon thin film;

(b) a step for ion implanting a dopant at a position corresponding to asemiconductor strain gauge of the silicon thin film to form a diffusionresistor, and forming devices necessary for circuit construction on thesilicon thin film;

(c) a step for providing a protective film on the entire surface of thewafer, opening a through hole penetrating the silicon thin film bypatterning and etching, and forming a weight part and a beam partconnecting to a support frame part remained on the periphery;

(d) while maintaining the protective film, as is, for forming thethrough hole, a step for removing by wet etching the SiO₂ layer underthe weight part and the beam part;

(e) a step for removing the protective film, and coating a resist overthe entire surface of the wafer;

(f) a step for forming a slit by dicing for dividing the chip whilemaintaining a small thickness of the wafer;

(g) a step for removing by ashing the resist on the wafer by an O₂plasma; and

(h) a step for dividing the chip by concentrating a stress on the slit.

According to a yet further aspect, there is provided a production methodof an angular acceleration sensor chip of the following processes.

Specifically, the production method of the angular acceleration sensorchip is characterized by comprising:

(a) a step for preparing a SOI wafer comprising a silicon substrate, aSiO₂ layer and a silicon thin film;

(b) a step for ion implanting a dopant at a position corresponding to asemiconductor strain gauge of the silicon thin film to form a diffusionresistor, forming a magnetic thin film at a position corresponding to aweight part, forming a detection coil surrounding the magnetic thinfilm, and forming devices necessary for circuit construction on thesilicon thin film;

(c) a step for providing a protective film on the entire surface of thewafer, opening a through hole penetrating the silicon thin film bypatterning and etching, and forming a beam part connecting to the weightpart and a support frame part remained on the periphery;

(d) while maintaining the protective film, as is, for forming thethrough hole, a step for removing by wet etching the SiO₂ layer underthe weight part and the beam part;

(e) a step for removing the protective film, and coating a resist overthe entire surface of the wafer;

(f) a step for forming a slit by dicing for dividing the chip whilemaintaining a small thickness of the wafer;

(g) a step for removing by ashing the resist on the wafer by an O₂plasma; and

(h) a step for dividing the chip by concentrating a stress on the slit.

According to a yet further aspect, there is provided a production methodof an acceleration sensor chip of the following processes.

Specifically, the production method of the acceleration sensor chip forconstructing a sensor structure on a third layer provided on a firstlayer of support substrate through an insulating second layer,characterized by comprising:

a first step for forming a plurality of cutouts of a same width on thethird layer to form a detection surface of the sensor structure having abeam part and a weight part for displacing the beam part which areseparated from each other;

a second step for filling the plurality of cutouts of the same width ofthe sensor structure with a sealing agent to flatten the surface of thethird layer including the sensor structure;

a third step for forming a circuit part connected electrically to thesensor structure in the periphery of the surface-flattened third layer;and

a fourth step for removing the sealing agent filled in the plurality ofcutouts of the same width and removing the second layer located beneatha detection surface of the sensor structure to make the beam part andthe weight part provided on the detection surface of the sensorstructure displaceable.

The above acceleration sensor chip production method may further have afifth step for coating a protective film on the surface of the thirdlayer including the sensor structure after the fourth step, forming aslit in the protective film-coated third layer, and performing dicing,and a sixth step for removing the protective film of the third layerafter dicing.

Further, in any one of the first step to the fourth step of theacceleration sensor chip production method, a film with a smallerthermal expansion coefficient than the material of the first layer maybe formed on the backside of the first layer.

Further, in the above acceleration sensor chip production method, thesame width of the plurality of cutouts formed on the sensor structuremay be a width of 2 μm or less.

Still further, in the above acceleration sensor chip production method,as a substrate comprising the first layer, the second layer and thethird layer, a silicon-on-insulator structure substrate may be used, ora substrate having polysilicon formed as the third layer on a singlecrystal silicon substrate through an insulation layer be used.

In accordance with the present invention, which attains the secondobject, there is provided a semiconductor sensor comprising asemiconductor sensor chip for detecting a physical value applied in adirection perpendicular to the surface of the chip and a package forincorporating the semiconductor sensor chip. In the package, a mainsurface for mounting the semiconductor sensor chip is formed to have apredetermined angle with respect to the surface of a printed circuitboard for mounting the package, the main surface is provided with aplurality of terminals along two opposite sides thereof for connectingwith input/output terminals of the semiconductor sensor chip, a bottomsurface perpendicular to the main surface is provided with a pluralityof pins respectively formed along the two sides parallel to the mainsurface, which plurality of pins are inserted into mounting holes formedin the printed circuit board, the plurality of terminals and theplurality of pins are electrically connected, and the input/outputterminals of the semiconductor sensor chip mounted on the main surfaceare electrically connected with the plurality of terminals of thepackage.

In this case, the main surface for mounting the semiconductor chip isformed substantially perpendicular to the surface of the printed circuitboard for mounting the package.

The semiconductor sensor chip may be a semiconductor acceleration sensorchip.

The semiconductor acceleration sensor chip may be any one of the abovedescribed acceleration sensor chips used to attain the first object.

Also, the semiconductor acceleration sensor chip may be the abovedescribed angular acceleration sensor chip used to attain the firstobject.

The semiconductor sensor package according to the present invention is apackage for incorporating a semiconductor sensor chip characterized inthat a main surface for mounting the semiconductor chip is formed at apredetermined angle with respect to the surface of a printed circuitboard mounting the package, the main surface is provided with aplurality of terminals along two opposite sides thereof for connectingwith input/output terminals of the semiconductor sensor chip, a bottomsurface perpendicular to the main surface is provided with a pluralityof pins respectively formed along the two sides parallel to the mainsurface, which plurality of pins are inserted into mounting holes formedon the printed circuit board, and the plurality of terminals and theplurality of pins are electrically connected along two side surfacessandwiching the main surface.

Here, the main surface for mounting the semiconductor sensor chip can beformed substantially perpendicular to the surface of the printed circuitboard mounting the package.

The wiring for connecting the plurality of terminals and the pluralityof pins is preferably buried in the package.

The above and the other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic perspective diagram showing a first example of aprior art acceleration sensor chip;

FIG. 1B is a schematic sectional diagram taken along line IB—IB of FIG.1A;

FIG. 2A is a diagram showing a second prior art example of anacceleration sensor ship;

FIG. 2B is a simplified plane diagram showing a comb electrode part ofFIG. 2A;

FIG. 3 is a schematic perspective diagram showing an example of priorart semiconductor sensor;

FIG. 4A is a schematic plane diagram showing the structure of a firstembodiment of the acceleration sensor chip according to the presentinvention;

FIG. 4B is a schematic sectional diagram taken along line IVB—IVB ofFIG. 4A;

FIG. 5A is a schematic enlarged plane diagram showing a sensor part ofthe acceleration sensor chip shown in FIGS. 4A and 4B;

FIG. 5B is a schematic sectional diagram taken along line VB—VB of FIG.5A;

FIG. 6 is a block diagram of an acceleration detection circuit in theacceleration sensor chip of the first embodiment;

FIGS. 7A to 7H are diagrams for explaining a production method of theacceleration sensor chip of the first embodiment;

FIG. 8A is a schematic plane diagram showing the structure of a secondembodiment of the acceleration sensor chip according to the presentinvention;

FIG. 8B is a schematic enlarged plane diagram showing a sensor part ofthe acceleration sensor chip shown in FIG. 8A;

FIG. 9 is a circuit diagram showing a Wheatstone bridge circuit in theacceleration sensor chip of the second embodiment;

FIG. 10 is a schematic plane diagram showing another structural exampleof the sensor part of the acceleration sensor chip shown in FIG. 8A;

FIG. 11A is a schematic plane diagram showing the structure of a thirdembodiment of the acceleration sensor chip according to the presentinvention;

FIG. 11B is a schematic sectional diagram taken along line XIB—XIB ofFIG. 11A;

FIG. 11C is a schematic enlarged diagram showing part of FIG. 11B;

FIG. 12 is a schematic enlarged plane diagram showing a sensor part ofthe acceleration sensor chip shown in FIG. 11A;

FIGS. 13A and 13B are schematic diagrams for explaining operationprinciple of the third embodiment;

FIGS. 14A to 14H are diagrams for explaining an acceleration sensor chipproduction method of the third embodiment;

FIG. 15 is a schematic plane diagram showing another structural exampleof a sensor part of the acceleration sensor chip of the thirdembodiment;

FIGS. 16A, 16B and 16C are respectively schematic plane diagrams showingthe structure of a fourth embodiment of the acceleration sensor chipaccording to the present invention;

FIG. 17 is a circuit diagram showing an example of circuit structure inthe acceleration sensor chip of the fourth embodiment;

FIG. 18 is a circuit diagram showing another example of circuitconstruction in the acceleration sensor chip of the fourth embodiment;

FIG. 19 is a schematic plane diagram showing the structure of an angularacceleration sensor chip as a fifth embodiment according to the presentinvention;

FIG. 20 is a circuit diagram showing an example of circuit constructionin the angular acceleration sensor chip of the fifth embodiment.

FIG. 21 is a plane diagram showing the surface structure of a sixthembodiment of the semiconductor sensor chip according to the presentinvention;

FIG. 22 is a sectional diagram taken along line XXII—XXII of FIG. 21;

FIG. 23 is a plane diagram showing the structure of a sensor part of anacceleration sensor chip as a sixth embodiment according to the presentinvention;

FIG. 24A is a sectional diagram taken along line XXIVA1'XXIVA of FIG.23;

FIG. 24B is a sectional diagram taken along line XXIVB—XXIVB of FIG. 23;

FIGS. 25A to 25D are process diagrams showing a production method of anacceleration sensor chip according to the present invention;

FIGS. 26A to 26E are process diagrams showing a production methodfollowing FIG. 25D;

FIGS. 27A and 27B are process diagrams for comparing etching steps of auniform cutout width and an irregular cutout width;

FIGS. 28A to 28C are process diagrams for explaining filling conditionwhen the cutout width is uniform;

FIGS. 29A to 29C are process diagrams for explaining filling conditionwhen the cutout width is irregular comparing with FIGS. 28A to 28C;

FIG. 30 is a block diagram showing the structure of an accelerationdetection circuit using the acceleration sensor chip according to thepresent invention;

FIG. 31 is a characteristic diagram explaining an effect of a backsidefilm.

FIG. 32A is a schematic diagram for explaining the semiconductor sensoraccording to the present invention, showing a front diagram of thesensor with the cover removed;

FIG. 32B is a schematic side diagram of the semiconductor sensor;

FIG. 32C is a sectional diagram taken along line XXXIIC—XXXIIC of FIG.32A;

FIG. 32D is a sectional diagram taken along line XXXIID—XXXIID of FIG.32A;

FIG. 33 is a schematic sectional diagram for explaining a mountingmethod of the semiconductor sensor according to the present invention toa printed circuit board;

FIG. 34 is a schematic diagram for explaining another example ofsemiconductor sensor according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, a SOI (silicon-on-insulator) wafer is used forthe acceleration sensor chip. While several methods are known in the artfor SOI wafer formation, for example a recrystallization method, anepitaxial growth method (SOS and the like), an insulation layerembedding method (SIMOX and the like), and a lamination method, a SOIwafer advantageously applicable to the present invention is formed by adirect joining technology utilizing an oxide film. Specifically, thesurface of a 500 to 700 μm thick first silicon substrate (supportsubstrate) is polished to a mirror surface, a several μm thick oxidefilm is formed on the surface of a second silicon substrate (movablepart formation substrate) of the same diameter, these two substrates areput together, and closely contacted substrates are heated in anoxidizing atmosphere to join the two substrates with each other. Then,the second substrate is ground and precision mirror polished to removean oxide film of the surface opposing the bonded surface and reduce thethickness of the second substrate to a predetermined value, for example,5 to 10 μm, thereby obtaining a desired SOI wafer.

On the thus obtained SOI wafer, a number of acceleration sensor chipsare collectively formed. Specifically, first, a sensor part havingformed thereon a movable part comprising a weight part and a beam part,a support frame part for supporting both parts, and a semiconductorstrain gauge, an amplifier circuit, a digital adjustment circuit,wiring, input/output terminals, and the like are formed on the secondsilicon substrate. Next, an insulation layer (sacrificial oxide film)under the movable part is removed by etching. Then, the wafer can bediced into discrete chips to fabricate a number of acceleration sensorchips.

In the acceleration sensor chip according to the present invention, thethin-walled movable part is formed on the second silicon substrate onthe thick-walled first silicon substrate, there is no problem withstrength due to the use of a large-diameter wafer. In particular, sincethe sensor part is small in size, has a resonant point at a highfrequency of about 40 to 80 kHz, and a wafer of 500 to 700 μm inthickness is used as the first silicon substrate, an excessivedisplacement or stress will never be applied to the thin beam part dueto a resonance of the wafer itself. Therefore, a number of sensor chipscan be collectively fabricated using a large-diameter wafer of 5, 6, or8 inches in diameter.

Embodiment 1

A first embodiment of the acceleration sensor chip according to thepresent invention is shown in FIGS. 4A, 4B, 5A and 5B. FIG. 4A is aschematic plane diagram showing the top of the acceleration sensor chip,FIG. 4B is a sectional diagram taken along line IVB—IVB of FIG. 4A, FIG.5A is an enlarged plane diagram of the sensor part, and FIG. 5B is asectional diagram taken long line VB—VB of FIG. 5A.

As shown in FIGS. 4A and 4B, a SiO₂ layer 102 to be an electricalisolation and sacrificial layer is formed between a silicon substrate100 and a silicon thin film 101, thus forming a chip. On the siliconthin film 101 of the chip, a sensor part 103 disposed at the center ofthe chip, a digital adjustment circuit 104, an analog amplifier circuit105, input/output terminals 106, and digital adjustment terminals 107are formed. The analog amplifier circuit 105 is for amplifying an outputof the sensor part 103. The digital adjustment circuit 104 is forperforming sensitivity compensation and temperature compensation of thesensor chip, which is formed, for example, of a ROM. The digitaladjustment terminals 107 are for inputting data for adjustment purposeto the digital adjustment circuit 104.

As shown in FIG. 5A, the sensor part 103 comprises a weight part 110,and protruded parts (beam parts) 111 a ₁, 111 a ₂, 111 b ₁, and 111 b ₂at four corners thereof, the weight part 110 is integrated with asurrounding support frame part 112 through the protruded parts (beamparts) 111 a ₁, 111 a ₂, 111 b ₁, and 111 b ₂ at the four corners. Inthis structure, the weight part 110 is supported by two sets of parallelbeams, that is, supported on the support frame part 112 by a first beamincluding the protruded parts 111 a ₁ and 111 a ₂ and a second beamincluding the protruded parts 111 b ₁ and 111 b ₂. Numeral 108 indicatesthrough holes penetrating the silicon thin film 101. Utilizing thesethrough holes, the SiO₂ layer 102 under the weight part 110 and the beamparts 111 a ₁, 111 a ₂, 111 b ₁, and 111 b ₂ is removed by wet etching(see FIG. 4B and FIG. 5B). As a result, the weight part 110 and thefirst and second beams are displaceable in a direction perpendicular tothe surface thereof.

The weight part 110 and the beam parts 111 a ₁, 111 a ₂, 111 b ₁, and111 b ₂ are equal in thickness, which is, for example, 5 μm. Dimensionsof the weight part 110 are, for example, 850 μm×600 μm, and width of thebeam parts is, for example, 30 μm. At respective support frame sides andweight part sides on both ends of the beam parts 111 a ₁, 111 a ₂, 111 b₁, and 111 b ₂, a total of 8 semiconductor strain gauges 113 a, 113 b,113 c, 113 d, 113 e, 113 f, 113 g, and 113 h are formed by dopantdiffusion. Wiring 114 connects these strain gauges, and a Wheatstonebridge is formed of the strain gauges. The Wheatstone bridge isconnected to a constant voltage power supply Vcc and a ground GND, andthe outputs V+ and V− thereof are conducted to the amplifier circuit105.

FIG. 6 shows a block diagram of an acceleration detection circuit.Outputs V+ and V− of the Wheatstone bridge composed of the eightsemiconductor strain gauges 113 a, 113 b, 113 c, 113 d, 113 e, 113 f,113 g, and 113 h are inputted and amplified in the amplifier circuit105. When an acceleration is applied in a direction of the arrow in FIG.5B, the strain gauges 113 b, 113 c, 113 f, and 113 g at the weight partside are subjected to a compressive stress to decrease their resistance,and the support frame part side strain gauges 113 a, 113 d, 113 e, and113 h are subjected to a tensile stress to increase their resistance. Asa result, a sensor output according to the magnitude of the accelerationis obtained from the Wheatstone bridge, which is amplified by theamplifier circuit 105. Further, data Vg for sensitivity compensation, adata TCS and an offset voltage Voff (sensor output when no accelerationis applied) for compensating the temperature characteristic ofsensitivity, and a data ΔVoff for compensating a deviation of the offsetvoltage are input from the digital adjustment circuit 104 to theamplifier circuit 105. Output of the amplifier circuit 105 is obtainedas an output Vout through a high-pass filter 116 and a low-pass filter117. Thus, a detection result which is compensated as necessary isdelivered as the bridge output voltage Vout. The high-pass filter 116and the low-pass filter 117 may be external circuits, or adjustmentparts of frequency response areas thereof may be incorporated in thedigital adjustment circuit 104.

In the present embodiment, the weight part 110 is movably supported onthe support frame part 112 by the two parallel beam parts 111 a and 111b formed on both sides. This prevents a measurement error due to atorsional deformation of the beam parts which can occur in a prior artacceleration sensor chip shown in FIGS. 1A and 1B. Further, in thepresent embodiment, since two strain gauges are disposed on one side ofthe bridge, sensitivity of the sensor chip can be enhanced. Stillfurther, in the present invention, since the Wheatstone bridge is formedof semiconductor strain gauges, even if foreign matter of a size thatdoes not disturb the movement of the weight part enters between thesensor part 103 and the silicon substrate 100, the influence on thesensor characteristic is small, unlike the capacitive type.

Yet further, the acceleration sensor chip of the present embodiment isprovided with a function to confirm whether or not the sensorperformance is normal, that is, a self-check function. This is performedas follows. Silicon of small resistivity is used as the siliconsubstrate 100, an electrode 115 provided on the backside (in FIG. 6, itis shown to be on the surface for convenience) is applied externallywith a voltage Vself to generate a potential difference between thesilicon substrate 100 and the silicon thin film 101, the sensor 103 isdisplaced by the electrostatic force, and an output from the bridge isdetected. The gap between the silicon substrate 100 and the silicon thinfilm 101 is determined by the thickness of the SiO₂ layer in between. Inother words, the gap size can be easily controlled by controlling thethickness Of SiO₂ layer in the production of the SOI wafer. Therefore,since the magnitude of the electrostatic force generated by an appliedvoltage can be easily and precisely calculated, self diagnosis(self-check) is possible by checking the relationship between themagnitude of an AC or DC voltage applied to the electrode 115 and thesensor output. Naturally, since dimensions of the movable partcomprising the weight part and the beam parts are determined at the timeof designing, a voltage range for generating a displacement that doesnot cause contact with the silicon substrate can be easily determined.

Next, a production method of the above-described embodiment will bedescribed with reference to FIGS. 7A to 7H. FIGS. 7A to 7H showcross-sections along line VII—VII of FIG. 5A.

As shown in FIG. 7A, a SOI wafer is prepared, which comprises thesilicon substrate 100 produced by the above-described direct joiningmethod, the SiO₂ layer 102, and the silicon thin film 101. In thepresent embodiment, a 6-inch diameter wafer is used, the siliconsubstrate 100, the SiO₂ layer 102, and the silicon thin film 101 havethicknesses of 625 μm, 1 μm, and 5 μm, respectively. In this state,boron or phosphorus is ion implanted at positions corresponding tosemiconductor strain gauges 113 a to 113 h of the silicon thin film 101to form diffusion resistors. The digital adjustment circuit 104, theanalog amplifier circuit 105, the terminals 106 and 107, wiring andother devices necessary for circuit construction are formed in thisstage on the silicon thin film 101.

As shown in FIG. 7B, a protective film 90 is provided on the entiresurface of the wafer, the through holes 108 penetrating the silicon thinfilm 101 are opened by patterning and etching (wet or dry etching) toform the weight part and the beam parts connecting the support framepart remaining on the periphery. At this time, the through holes 108 arealso formed in the weight part.

As shown in FIG. 7C, the protective film 90 for forming the throughholes 108 remains, as is, the SiO₂ layer 102 under the weight part andbeam parts is removed by wet etching using buffered hydrofluoric acid(HF+NH₄F)

As shown in FIG. 7D, the protective film is removed, and a resist 118 iscoated again on the entire wafer surface using a spinner. This resist isto protect the sensor part and circuits in the subsequent dicingprocess, and also to prevent foreign matters from entering the gapformed between the sensor part and the silicon substrate.

As shown in FIG. 7E, by dicing, slits 119 for dividing the chip areformed while remaining a small thickness of the wafer.

As shown in FIG. 7F, the resist on the wafer is removed by washing usingan O₂ plasma.

As shown in FIG. 7G, the chip is divided using a tool 120 forconcentrating a stress on the slits 119.

As a result, as shown in FIG. 7H, a divided chip 121 is completed.

Thus, a number of acceleration sensor chips can be collectively producedfrom a large diameter wafer, and foreign matter can be prevented fromentering the gap between the silicon substrate and the movable part ofthe sensor during the production process.

Embodiment 2

A second embodiment of the acceleration sensor chip according to thepresent invention is shown in FIGS. 8A, and 8B. FIG. 8A is a topdiagram, and FIG. 8B is an enlarged diagram of the sensor part.

As shown in FIG. 8A, a chip is constructed in a manner similar to thatshown in FIGS. 4A and 4B. On the silicon thin film 101 of the chip, asensor part 200 disposed at the center of the chip, a digital adjustmentcircuit 104, an analog amplifier circuit 105, input/output terminals 106and digital adjustment terminals 107 are formed. The present embodimentdiffers from the first embodiment in the structure of the sensor partand the layout of semiconductor strain gauges in association with thesensor part structure. Since other parts are the same as the firstembodiment, detailed description thereof is omitted.

As shown in FIG. 8B, the sensor part 200 comprises two weight parts 201a and 201 b, and six connection parts 211 a ₁, 211 a ₂, 211 a ₃, 211 b₁, 211 b ₂, and 211 b ₃ for connecting a support frame part 212 and forconnecting the two weight parts and a support frame part 212 and forconnecting the two weight parts with each other. The two weight partsand the periphery thereof are provided with the through holes as in theweight part of the embodiment 1, and the SiO₂ layer under the two weightparts and the six connection parts is removed by etching. Therefore, thetwo weight parts are integrated with the peripheral support frame part212 through the connection parts 211 a ₁, 211 a ₃, 211 b ₁, and 211 b ₃,thus being displaceable in a direction perpendicular to the papersurface. In this structure, the two weight parts 201 a and 201 b aresupported on the support frame part 212 by two parallel beams, that is,a first beam including the connection parts 211 a ₁, 211 a ₂, and 211 a₃, and a second beam including the connection parts 211 b ₁, 211 b ₂,and 211 b ₃.

Semiconductor strain gauges 213 a, 213 b, 213 c, and 213 d are formed bydopant diffusion on the connection parts 211 a ₁ and 211 a ₂ of thefirst beam, and on the connection parts 211 b ₂ and 211 b ₃ of thesecond beam, respectively. To increase the sensitivity, thickness of thebeam is preferably smaller than the thickness of the weight part(thickness of the silicon thin film). In the present embodiment, thebeam has a thickness of 2 μm while the weight part has a thickness of 5μm.

The acceleration sensor chip of the present embodiment can be producedby the same process as in the first embodiment. However, to reduce thethickness of the beam, in the above process (a), before forming thesemiconductor strain gauges, circuit devices and the like, the thicknessof the beam is decreased by way of pattern etching.

FIG. 9 shows the Wheatstone bridge circuit in the present embodiment.When an acceleration in a direction towards the silicon substrate isapplied in the thickness direction of the weight part of theacceleration sensor chip shown in FIG. 8B, to the part where thesemiconductor strain gauges 213 b and 213 c are formed in the connectionparts, a compressive stress is applied, and to the part where thesemiconductor gauges 213 a and 213 d are formed, a tensile stress isapplied. Therefore, the semiconductor strain gauges 213 b and 213 c aredecreased in resistance, and the semiconductor strain gauges 213 a and213 d are increased in resistance. With these actions, a voltage changeaccording to the acceleration change is output from the Wheatstonebridge circuit.

FIG. 10 shows another example of construction of the sensor part havingtwo weight parts. Unlike the sensor part shown in FIG. 8B, the weightparts 201 a and 201 b are connected to the support frame part by threesets of parallel beams defined by beam parts 211 c ₁ and 211 c ₂, 211 d₁ and 211 d ₂, 211 e ₁ and 211 e ₂. The weight parts 201 a and 201 bare, as in the example of FIG. 8B, connected by two parallel beam parts211 a and 211 b. The beam parts 211 d ₁, 211 a, 211 b and 211 d ₂ areprovided with semiconductor strain gauges 213 a, 213 b, 213 c, and 213d, thereby forming a Wheatstone bridge. Since a stress is generated onthe surface of the beam part by an acceleration, to increase thestability of wiring, as wiring for connecting the respective straingauges, a normal Al wiring structure (Al wiring is provided on siliconthrough an insulation layer) is not used, but a diffusion wiring may beused. In this case, the diffusion wiring is a sheet resistor, and thevalue is determined by the length and width. In the example shown inFIGS. 8A and 8B, in the part where a strain gauges are formed of beampart connecting the weight part and the support frame part, two wiringsare necessary on a single beam part, therefore the wiring becomes smallin width, the sheet resistor increases in resistance, and thesensitivity is reduced to this extent. On the other hand, in an examplein FIG. 10, a single wiring is sufficient for each beam, therefore thewiring width can be widened, and a low resistance wiring can be used,thereby reducing the decrease of sensitivity.

Further, since the present embodiment is constructed by such aWheatstone bridge, any combination may be used which provides theequivalent gauge change, therefore the present embodiment is not limitedto the gauge layout and gauge combination shown in FIGS. 8A, 8B, andFIGS. 9, 10.

Embodiment 3

A third embodiment of the acceleration sensor chip according to thepresent invention is shown in FIGS. 11A, 11B, and 11C. FIG. 11A is aplane diagram of the top of the sensor, FIG. 11B is a sectional diagramtaken along line XIB—XIB of FIG. 11A, and FIG. 11C is an enlargeddiagram of the sensor part shown in FIG. 11B.

As in the first embodiment, a SiO₂ layer 102 for electrical isolationand as a sacrificial layer is formed between the silicon substrate 100and the silicon thin film 101, thus forming a chip. On the silicon thinfilm 101, a sensor part 300, a digital adjustment circuit 104, an analogamplifier circuit 105, input/output terminals 106 and digital adjustmentterminals 107 are formed. The SiO₂ layer under the sensor part 300disposed at the center of the chip is removed by etching as inembodiments 1 and 2. As will be described later, for self-checking, thesensor part can be displaced by applying a voltage between the siliconsubstrate 100 and the sensor part 300.

An enlarged top diagram of the sensor part is shown in FIG. 12. Thesensor part 300 comprises a weight part (302) on which a magnetic thinfilm 301 of a NbFeB type or SmCo type or the like as a thin film magnetis formed on the surface of the silicon thin film using a vacuumdeposition method or sputtering method or the like, and an elastic beampart 303 for connecting the weight part and the support frame part 112.The SiO₂ under the sensor part is removed as described above, and thesilicon thin film on the periphery of the sensor part is also removed toform a through hole for sacrificial layer etching. The weight part 302having the magnetic thin film 301 on the surface is integrated with thesupport frame part through the elastic beam 303. When an accelerationperpendicular to the paper surface is applied to the weight part 302,the elastic beam 303 is deflected, and the weight part is displaced. Onthe support frame part at the periphery of the through hole 108, adetection coil 304 surrounding the weight part is formed using a thinfilm technique.

FIGS. 13A and 13B are diagrams for explaining the operation principle ofthe present embodiment. As shown in FIG. 13A, when an acceleration G isapplied to the sensor chip, the weight part 302 and hence the magneticthin film 301 is displaced upward, and, according to Lenz's law, acurrent I flows in the detection coil 304 in association with a changein acceleration of the magnetic thin film 301. On the other hand, whenthe magnetic thin film is displaced downward as shown in FIG. 13B, acurrent in the direction reverse to that shown in FIG. 13A flows in thedetection coil 304. The thus generated induction current can be inputtedto an integration circuit or the like to detect an acceleration, to atwo-stage integration circuit to detect a velocity, and to a three-stageintegration circuit to detect a displacement.

A production method of the present embodiment is shown in FIGS. 14A to14H. FIGS. 14A to 14H are respective sectional diagrams corresponding toFIG. 11B.

As shown in FIG. 14A, a SOI wafer is prepared, which comprises thesilicon substrate 100 produced by the above-described direct joiningmethod, the SiO₂ layer, and the silicon thin film 101. In this state,the magnetic thin film 301 is formed at the position corresponding tothe weight part of the silicon thin film by a vacuum deposition methodor a sputtering method, and a detection coil is formed on the periphery.The digital adjustment circuit 104, the analog amplifier circuit 105,the terminals 106 and 107, wiring and other devices necessary forcircuit construction are formed in this stage on the silicon thin film101.

As shown in FIG. 14B, a protective film 90 is provided on the entiresurface of the wafer, the through holes 108 penetrating the silicon thinfilm 101 are opened by patterning and etching (wet or dry etching) toform the weight part 302 and the elastic beam part 303 connecting to thesupport frame part are formed.

As shown in FIG. 14C, the protective film 90 for forming the throughholes 108 is maintained, as is, and the SiO₂ layer 102 under the weightpart and beam part is removed by wet etching using buffered hydrofluoricacid.

As shown in FIG. 14D, the protective film is removed, and a resist 118is coated on the entire wafer surface using a spinner. This resist is toprotect the sensor part and circuits in the subsequent dicing process,and also to prevent foreign matter from entering the gap formed betweenthe sensor part and the silicon substrate.

As shown in FIG. 14E, by dicing, slits 119 for dividing the chip areformed while maintaining a small thickness of the wafer.

As shown in FIG. 14F, the resist on the wafer is removed by ashing usingan O₂ plasma.

As shown in FIG. 14G, the chip is divided using a tool 120 forconcentrating a stress on the slits 119.

As a result, as shown in FIG. 14H, a divided chip 121 is completed.

Thus, a number of acceleration sensor chips can be collectively producedfrom a large diameter wafer, and foreign matter can be prevented fromentering the gap between the silicon substrate and the movable part ofthe sensor during the production process.

FIG. 15 shows another construction example of the sensor part. Theweight part 302 having the magnetic thin film 301 formed on the surfaceis supported by a plurality of elastic beams 303 a and 303 b. In thiscase, displacement of the weight part, and hence the magnetic thin film301, is in a direction perpendicular to the paper surface.

Embodiment 4

A fourth embodiment of the acceleration sensor chip according to thepresent invention is shown in FIGS. 16A, 16B, and 16C. In the presentembodiment, the sensor parts of the above third embodiment are connectedin series. When a signal of a single sensor is amplified, in the case ofthe sensor by an ordinary semiconductor strain gauge, an electrostaticcapacitive type sensor chip or the like, it is generally amplified by anamplifier circuit. However, in the case of the acceleration sensor chipof the present embodiment, due to its construction, by connecting aplurality of sensors in series, it is possible to amplify the signal byproviding a number of connected sensors. FIG. 16A shows a lowacceleration sensor chip 401 connecting a large number of sensor parts300, FIG. 16B shows a medium acceleration sensor chip 402 connecting amedium number of sensor parts 300, and FIG. 16C shows a highacceleration sensor chip 403 comprising a single sensor part 300.Further, when a plurality of sensors differing in detection range areformed on a single chip, and outputs of the plurality of sensors areselected and inputted to an amplifier, a single acceleration sensor chipcan be used for detection of acceleration over a wide range.

A circuit construction example of the present embodiment is shown inFIGS. 17 and 18. In both figures, only two detection coils of two sensorparts are shown for simplicity. An induction current induced in thedetection coil 304 of the sensor part 300 is converted to a voltageoutput by a voltage conversion resistor 411 and output to the outsidethrough the amplifier circuit 105 having been adjusted by the digitaladjustment circuit 104, a high-pass filter 116, a low-pass filter 117and the like. FIG. 17 shows an example in which the digital adjustmentcircuit 104 and the amplifier circuit 105 are provided at a positionother than on the chip on which the sensor part is formed, and FIG. 18shows an example in which these parts are formed on the same chip as thesensor part.

In the present embodiment, as shown in FIG. 11C, self-checking ispossible by which the sensor chip is moved by an electrostatic forcegenerated when a voltage is applied between the silicon substrate 100and the sensor part 300, and an induction current induced in thedetection coil according to the movement at that time of the sensor partis amplified by the amplifier circuit 105. Further, in the presentembodiment, it is also possible to perform self-checking using selectswitches 412 and 413 for selecting an ordinary acceleration detectionand self-checking. That is, the switches are selected so that a currentflows to the detection terminals 414 and 415, and to the self-checkterminal 416 in self-checking. In self-checking, the detection coils 304are supplied with a pulse output to give the sensor part 300 animpulsive electromagnetic force to move the weight part 302, a responseat that time is processed and checked by the circuits after theamplifier circuit, thereby performing the self-checking. According tothese methods, the self-checking function can be achieved by a simplesensor construction. Still further, in addition to the above methods, itis also possible to perform self-checking by a method in which apermanent magnet or an electromagnet is disposed in the vicinity of thesensor part 300, a magnetic field is applied externally to the sensorpart, and an induction current generated in the detection coils 304 whensensor part is moved by the magnetic field is detected.

It is needless to say that these self-checking functions can be providedto the acceleration sensor chip of the third embodiment.

Embodiment 5

A fifth embodiment of the present invention is shown in FIG. 19. Thefifth embodiment combines two units of the third embodiment shown inFIG. 11 or the fourth embodiment shown in FIG. 16 to detect an angularacceleration. In FIG. 19, three units each of sensors 300L and 300R aredisposed symmetrically on the left and right of a detection axis 500.When an angular acceleration changes about the detection axis, forexample, the weight part displaces upward in the left side sensor, andthe weight part displaces downward in the right side sensor.

As shown in FIG. 20, these sensors are wired to form a closed loop sothat currents in the same directions flow in the detection coils 304Land 304R of the left and right sensor arrays when a change in angularacceleration generates about the detection axis 500. This current, as inthe fourth embodiment, is converted into a voltage by the voltageconversion resistor 411, integrated and amplified. This enables thesensor chip to be used as an angular acceleration sensor chip fordetecting an angular acceleration generated about the detection axis500.

Embodiment 6

FIGS. 21 and 22 shows the entire construction of an acceleration sensorchip according to a sixth embodiment of the present invention.

FIG. 22 is a sectional diagram of along the XXII—XXII line of FIG. 21.In FIG. 22, the sensor chip comprises a silicon substrate (hereinafterreferred to as Si substrate) 600 as a first layer, a sacrificial layer602 comprising SiO₂ as a second layer, and a silicon active layer(hereinafter simply referred to as active layer) 601 as a third layer.The active layer 601 is electrically separated from the Si substrate 600by the sacrificial layer 602. Further, the Si substrate 600 is providedwith a backside oxide film 612 formed on the backside located at theopposite side of the active layer 601. The backside oxide film 612comprises a film which has a smaller thermal expansion coefficient thanthe silicon material of the first layer, for example, SiO₂, SiN or thelike.

FIG. 21 shows a surface state of the active layer 601. The active layer601 is provided with a circuit part comprising a sensor part 603disposed at the center of the chip, a digital adjustment circuit 604disposed on the periphery of the sensor part 603, an analog amplifiercircuit 605, an input/output terminal 606, a digital adjustment terminal607, and the like. The analog amplifier circuit 605 is a circuit foramplifying output of the sensor part 603, the digital adjustment circuit604 is a circuit for performing sensor sensitivity correction,temperature correction, and the like, composed of, for example, a ROM.Further, the digital adjustment terminal 607 is a terminal for inputtingdata into the digital adjustment circuit 604.

FIG. 23 shows the structure of the sensor part 603. The sensor part 603comprises a displaceable detection surface 700, and a support frame part800 connected with the detection surface 700. The detection surface 700comprises weight parts 610 a and 610 b, and beam parts 611 a, 611 b, 611c, 611 d, 611 f, 611 g, and 611 h. The weight parts 610 a and 610 b areprovided with a plurality of through holes (cutouts) 608 a and aplurality of slits (cutouts) 608 b and are divided along the slitformation direction at the center. The weight parts 610 a and 610 b areconnected with the beam parts 611 d and 611 e, and the weight parts 610a and 610 b are connected with the surrounding support frame part 800through the beam parts 611 a, 611 b, 611 c, 611 f, 611 g, and 611 h. Thesupport frame part 800 is integrated with the active layer 601.

Further, the through holes 608 a and the slits 608 b provided on thesacrificial layer 602 are respectively for removing SiO₂ layer of thesacrificial layer 602 opposing the weight parts 610 a and 610 b and thebeam parts 611 a, 611 b, 611 c, 611 d, 611 e, 611 f, 611 g, and 611 hand for separating the outer shape of the sensor part 603 from theactive layer 601. Still further, a width or side of the through hole 608a and a width of the slit 608 b are constant (in the present embodiment,a width of 2 μm or less, however, the width not limited to thisparticular value). In the detection surface 700 comprising the weightparts 610 a and 610 b and the beam parts 611 a, 611 b, 611 c, 611 d, 611e, 611 f, 611 g, and 611 h, the sacrificial layer 602 of the lower partis removed, thereby making the detection surface 700 displaceable in adirection perpendicular to its surface.

Here, the weight parts 600 a and 610 b and the beam parts 611 a, 611 b,611 c, 611 d, 611 e, 611 f, 611 g, and 611 h are equal in thickness, forexample, 5 μm. Size of the weight parts 610 a and 610 b is set to, forexample, 250 μm×850 μm and the width of the beam parts 611 a, 611 b, 611c, 611 d, 611 e, 611 f, 611 g, and 611 h is set to, for example, 30 μm.In the beam parts 611 b, 611 d, 611 e, and 611 g, a total of foursemiconductor strain gauges 613 a, 613 b, 613 c, and 613 d are formed bydopant diffusion, and by these four strain gauges, a Wheatstone bridgeis formed as will be shown in FIG. 30 described later. The Wheatstonebridge is connected to a constant voltage power supply Vcc and a groundGND, and its output is conducted to V+ and V−. Further, the backsideoxide film 112 has a thickness of, for example, 0.25 μm.

FIG. 24A is a XXIVA—XXIVA sectional diagram of FIG. 23. FIG. 24B is aXXIVB—XXIVB sectional diagram of FIG. 23. FIG. 24A is a sectionaldiagram at a position passing through the through hole 608 a of theweight part 610 a and 610 b constituting the detection surface. FIG. 24Bis a sectional diagram taken at a position passing through the slit 608b of the beam parts 611 a, 611 b, 611 c, 611 d, 611 e, 611 f, 611 g, and611 h.

Next, a production method of the acceleration sensor chip of the sixthembodiment of the present invention will be described with reference toFIGS. 25 and 26.

In a first step of FIG. 25A, a SOI wafer is prepared which comprises asingle crystal Si substrate 600, a SiO₂ sacrificial layer 602, and asingle crystal Si active layer 601. In the present embodiment, a 6 inchdiameter wafer is used, the Si substrate 600 has a thickness of 625 μmthe sacrificial layer 602 is 1 μm in thickness, and the active layer 601is 5 μm in thickness.

In a second step of FIG. 25B, a plurality of through holes 608 a and aplurality of slits 608 b for forming weight parts 610 a and 610 b andbeam parts 611 a, 611 b, 611 c, 611 d, 611 e, 611 f, 611 g, and 611 hare formed by etching. In this case, by performing trench processing byRIE, plasma etching, wet etching or the like, the through holes 608 aand the slits 608 b can be formed with a uniform width of 2 μm or lessover the entire surface of the detection surface, and the etching widthreaches the insulation layer 602. Areas other than the etching area arecoated previously with a protective film 630 on the surface, which isremoved after completion of the etching processing.

In a third step of FIG. 25C, the etched through holes 608 a and slits608 b are filled with oxide film 650 and polysilicon 651. In thefilling, first the oxide film 650 is formed inside the slit 608 b and onthe surface of the active layer 601.

Formation of the oxide film 650 is performed using a diffusion furnaceor the like. Next, on the surface on which the oxide film 650 is formed,polysilicon 651 is formed using CVD (Chemical Vapor Deposition) or thelike. Thickness of the thus formed film, as an optimum film thicknessfrom experience, is about 1 μm. The surface of the active layer 601 towhich the oxide film 650 and polysilicon 651 are adhered is flattened byetching (plasma etching or wet etching or the like).

With the thus flattened SOI wafer surface, boron or phosphorus is ionimplanted (or thermally diffused) at positions corresponding tosemiconductor strain gauges 613 a, 613 b, 613 c, and 613 d in the sensorpart 603 of the active layer 601 to form diffusion resistors.

Further, in the processing after flattening, a digital adjustmentcircuit 604, an analog amplifier circuit 603, terminals 606 and 607,wiring 609 and other devices necessary for circuit construction are alsoformed on the surface of the active layer 601 at the same time.Alternatively, the circuit part can be constructed using an ordinaryprocess, for example, one which is used when constructing C-MOS.

In a fourth step of FIG. 25D, a protective film 631 is provided over theentire surface of wafer, after patterning, SiO₂ of the insulation layer602 opposing the positions of the weight parts 610 a and 610 b and thebeam parts 611 a, 611 b, 611 c, 611 d, 611 e, 611 f, 611 g, and 611 h isremoved by etching with an etching solution using buffered hydrofluoricacid (HF+NH₄F). At the same time, the oxide film 650 and the polysilicon651 are removed by etching. Also, the oxide film 650 and the polysilicon651 may be removed by plasma etching with SF₆+O₂ mixed gas. After that,the backside oxide film 612 is formed on the silicon substrate 600.Formulation of the backside oxide film 612 is not limited to the fourthstep, but may be formed in any of first to fourth steps.

Next, FIGS. 26A to 26E are steps following above FIGS. 25A to 25D.

In a fifth step of FIG. 26A, the protective film 631 is removed, andthen the entire wafer surface is again coated with a protective film 618such as a resist using a spinner. The protective film 618 is forprotecting the sensor part 603 and the circuit part in the subsequentdicing step, and for preventing foreign matter from entering the gapformed between the sensor part 603 and the substrate 600.

In a sixth step of FIG. 26B, slits 617 are formed by dicing for dividingthe chip while remaining a small thickness of the wafer.

In a seventh step of FIG. 26C, the protective film 618 on the wafersurface is removed by ashing using an O₂ plasma.

In an eighth step of FIG. 26D, the chip is divided using a tool 620 toconcentrate a stress on the slits 617.

In a ninth step of FIG. 25E, the thus divided chip is completed.

As described above, when fabricating the sensor part, by forming thethrough holes 608 a and slits 608 b of a constant width (e.g., less than2 μm) over the entire detection surface, etching can be efficientlycarried out and filling with polysilicon 651 or the like be performeduniformly over a large area. This allows for fabricating a number ofsensor chips using not only the prior art 4-inch wafer but also alarge-diameter wafer of 5 or 6 inches in diameter (for example, about500 to 600 μm in thickness). The process also prevents foreign matterfrom entering the gap between the substrate 600 and movable parts of thesensor part 603 (weight parts and beam parts) during the fabricationprocess.

Further, a latent internal stress in the SOI wafer can be balanced byforming the backside oxide film 612, whereby suppressing as possible astrain and stress generated in the sensor part 603.

Next, the reason why in the above production method, the width of thecutouts formed over the entire surface of the sensor part 603, that is,the width of the through holes 608 a and slits 608 b are a constantvalue, and the width is 2 μm or less will be described with reference toFIGS. 27, 28, and 29.

First, FIG. 27A shows an example when the width is uniformly formed inthe second step of the present invention. FIG. 27B is an example whenthe width is irregular. When the width is uniform as in the presentinvention of FIG. 27A, etching is made in a same depth, however, whenthe width is irregular as in FIG. 27B, an unetched part is generatedeven after passage of a time, and this tendency becomes more apparent asthe area of the detection surface to be etched becomes large. Therefore,in the present invention, the width of the through hole 608 a and theslit 608 b is formed in a constant value.

Further, FIGS. 28A to 28C show an example when the width in the thirdstep of the present invention is formed in a uniform value of 2 μm orless. FIGS. 29A to 29C show an example when the width is irregular. Now,if the width is assumed as 2 μm, in the present invention, in the stagewhere the oxide film 650 of FIG. 28A is formed, in consideration of thefilm thickness, the width of the through hole 608 a and the slit 608 bis about 1.8 μm. When polysilicon 651 of FIG. 28B is formed to athickness of about 1 μm on the active layer 601, adherence advances byeach about 0.91 μm simultaneously from the surfaces of the opposingsides on the inner wall surface of the through holes 608 a and the slits608 b, in the stage where the holes are filled with polysilicon 651,also on the active layer 601, polysilicon 651 is adhered in a desiredthickness of about 1 μm .

On the other hand, when the width is irregular, as in FIG. 29, when theoxide film 650 is formed, there exists an area where the width of thethrough hole 608 a and the slit 608 b is over 2 μm. In such a state,when polysilicon 651 is formed in a film thickness of about 1 μm, asshown in FIG. 29B, in the through hole 608 a and the slit 608 b, thereis an area of not completely filled, and partial hollow 640 isgenerated.

In the present invention, when the surface of the active layer 601 isflattened by etching, as in FIG. 28C, the hole part is completely filledand flattened. However, in the case of FIG. 29C, the hollow 640 remains.Therefore, for the above reasons, the width of the through hole 608 aand the slit 608 b in the present invention is set to 2 μm or less overthe entire surface of the sensor part 603.

Next, construction of an acceleration detection circuit using the aboveacceleration sensor chip will be described with reference to FIG. 30.

Outputs V+ and V− of a Wheatstone bridge composed of four semiconductorstrain gauges 613 a, 613 b, 613 c, and 613 d are inputted in andamplified by an amplifier circuit 605. In this case, when anacceleration is applied in a perpendicular direction from the surface onwhich the sensor part 603 is formed towards the Si substrate 600 side,the strain gauges 613 b and 613 d formed on the beam parts 611 d and 611e between the weight parts 610 a and 610 b are subjected to acompressive stress and decrease in resistance, and the strain gauges 613a and 613 c formed on the beam parts 611 b and 611 g between the weightparts 610 a and 610 b and the active layer 601 as the peripheral supportpart are subjected to a tensile stress and increase in resistance. As aresult, a sensor output according to the magnitude of acceleration isobtained from the Wheatstone bridge, which is amplified by the amplifiercircuit 605.

Further, from the digital adjustment circuit 604, data Vg forsensitivity correction, data TCS for correcting temperaturecharacteristic of sensitivity, offset voltage Voff (sensor output whenno acceleration is applied), and correction value ΔVoff for correctingdeviation of offset voltage are inputted in the amplifier circuit 605.Output of the amplifier circuit 605 is obtained as an output Voutthrough a high-pass filter 626 and a low-pass filter 627.

Thus, a detection result that is corrected as necessary can be obtainedas bridge output voltage Vout. The high-pass filter 626 and the low-passfilter 627 may be external circuits. Their frequency response areaadjustment parts and the like may be incorporated in the digitaladjustment circuit 604. In the sensor chip constructed with these parts,when the through hole 608 a and the slit 608 b are formed, depthsthereof are processed uniformly, and the outer shape of the sensor part603 can be formed with good precision. Further, due to the backsideoxide film 612 formed on the substrate 600, any latent internal stressin the SOI can be balanced, thereby reducing strain to the sensor part603.

Next, the effect of the backside oxide film 612 will be described withreference to FIG. 31.

FIG. 31 shows a result confirmed by FEM (finite element method)analysis. Strain distribution and stress distribution in a thicknessdirection between A-B (see FIG. 23) parallel to the surface of theactive layer 601, obtained by FEM analysis, are shown. In this case,part of 0.2 mm to 0.8 mm in the position of the abscissas corresponds tothe sensor part 603. Strain with no backside oxide film 612 is shown asC-1 (--), and stress as C-2 (-∘-). When the thickness of the backsideoxide film 612 is 0.5 μm, strain is D-1 (-▪-), and stress is D-2 (-□-).When the thickness of the backside oxide film 612 is 0.25 μm, strain isE-1 (-▴-), and stress E-2 (-Δ-). From these results of analysis, in thecase of the present embodiment, strain and stress generated in thesensor part can be minimized by setting the thickness of the backsideoxide film 612 to 0.25 μm.

In the present embodiment, using the above SOI wafer, the accelerationsensor chip for making detection by the semiconductor strain gauge hasbeen described, however, the present invention is not limited to this.In addition to the above, the present invention can also be appliedsimilarly, for example, to a capacitive type sensor using SOI wafer anda capacitive type sensor using wafer in which polysilicon is formed as athird layer on a single crystal silicon substrate through an insulationlayer. Further, when applied to the capacitive type sensor, describedwith reference to FIG. 2B, the sensor chip can be fabricated by forminga cutout (hole or the like) disposed at the center of the displaceablefirst support body 13, especially in the area of straight mass body 15.

Embodiment 7

The present embodiment describes an example of the semiconductor sensoraccording to the present invention, which is shown in FIG. 32. FIG. 32Ais a front diagram, FIG. 32B is a side diagram, FIG. 32C is a sectionaldiagram taken along line XXXIIC—XXXIIC of FIG. 32A, and FIG. 32D is asectional diagram taken along line XXXIID—XXXIID of FIG. 32A. FIG. 32Ashows a state with a cover 921 shown in FIG. 32C removed.

For example, a package 920 made of epoxy resin has a sensor fixingsurface 920A for fixing a semiconductor sensor chip 910, a cover 921,and a plurality of pins 922 disposed in parallel along two side surfacessandwiching the sensor fixing surface 920A and protruding from a packagebottom surface with part thereof buried in a package main body. Thesensor fixing surface 920A is provided with a plurality of wire bondpads 923 for supplying current to the acceleration sensor chip andleading a detection signal to the outside. Each of the wire bond pads923 is connected to each of the pins 922 with wiring 925. In practice,the wire bonding pad 923 and the wiring 925 can be formed of an integralmetal thin plate. That is, a metal thin plate is punched into a desiredform, subjected to bending to be bonded to the sensor fixing surface920A and the package side surface, and connected with the pin 922 bysoldering. Further, the outer peripheral surface of the package iscoated with epoxy resin or the like to bury the wiring part in thepackage, which is preferable in view of protection of wiring. Thesemiconductor sensor chip 910 is fixed to the sensor fixing surface 920Aof the thus fabricated package with an adhesive or the like. Thesemiconductor sensor chip 910 is a sensor chip for detecting a physicalvalue, for example, an acceleration, applied in a direction 930perpendicular to its surface. The wire bond pad 923 is electricallyconnected to an input/output terminal (not shown) of the semiconductorsensor chip 910. In the present example, connection by wire bondingusing a wire 924 is shown. Finally, the cover 921 is bonded to thepackage main body. A semiconductor sensor is thus fabricated. Thisstructure is similar to a package structure known as DIP (dual in-linepackage). As shown, each of the plurality of pins 922 is constructedindependent of others in the package, so that the respective pins do notinterfere with each other. Further, since the wiring 925 is buried inthe package, it will never vibrate. Still further, since the package 920is sealed with the cover 921, the semiconductor sensor chip 910 willnever be exposed to the external environment.

As described above, the semiconductor sensor packaged with asemiconductor sensor chip 910 is mounted to a printed circuit board 940as in ordinary IC parts. FIG. 33 explains the mounting of the sensorchip package 920 on a printed circuit board 940, showing a cross sectioncorresponding to FIG. 32D. The pins 922 of the package 920 are insertedin mounting through-holes 941 of a printed circuit board 940, and bondedwith a solder 942 or the like from the lower surface of the printedcircuit board. With this method, the semiconductor sensor can be mountedto the printed circuit board by quite the same method as mounting ofDIP. The input terminal of the semiconductor sensor chip is connected toa power supply by a wiring (not shown) connected with the mountingthrough-holes 941 of the printed circuit board 940, and a signalcorresponding to the physical value detected by the semiconductor sensorcan be outputted to the outside. When detecting the physical value, theprinted circuit board is disposed so that the sensor chip surface of thesemiconductor sensor mounted to the printed circuit board opposescorrectly to the direction of the physical value to be detected.

By mounting the semiconductor sensor using the above-described package,the mounting area on the printed circuit board can be considerablyreduced, and the semiconductor sensor can be fixed so that thesemiconductor sensor chip is in line with the direction of physicalvalue to be detected, that is, the direction perpendicular to thesurface of the semiconductor sensor chip is parallel to the surface ofthe printed circuit board, and in line with the arrangement direction ofthe plurality of mounting through-holes.

The semiconductor sensor chip 910 sealed in the package 920 isconstructed in an integral silicon substrate, for example, as shown inFIG. 3, which may be an acceleration sensor chip for detecting anacceleration generated in a direction 70 perpendicular to the sensorchip surface, or be an acceleration sensor chip described in JapanesePatent Application Laid-open No. 5-273229 (1993) or its correspondingU.S. Pat. No. 5,490,421. However, the acceleration sensor chip and theangular acceleration sensor chip set forth are most acceptable forassembling the semiconductor sensor according to the present invention.

The present invention can be applied not only to the above-describedacceleration sensor and angular acceleration sensor but also to asemiconductor sensor for detecting physical values in which directivityis important. Further, in the semiconductor sensor shown in FIG. 33, anexample is shown in which the main surface for mounting thesemiconductor sensor chip is substantially perpendicular to the surfaceof the printed circuit board for mounting the package. However, theangle of the main surface for mounting the semiconductor sensor chipwith respect to the surface of the printed circuit board for mountingthe package can be flexibly selected in relation to the direction of thephysical value to be detected and the mounting position of the printedcircuit board constituting the sensor assembly.

FIG. 34 shows an example thereof, in which a direction 930 of physicalvalue applied perpendicular to the surface of the semiconductor sensorchip is 45 degrees with respect the a printed circuit board 940. Sincereference numerals are similar to those in FIG. 33, detailed descriptionthereof is omitted. In this case, the main surface of the semiconductorsensor package for mounting the semiconductor sensor chip 910 is in adirection of 45 degrees with respect to the printed circuit board 940.As shown, the main surface of the package mounting the semiconductorsensor chip for detecting a physical value applied in a directionperpendicular to the surface of the semiconductor sensor chip isselected in consideration of the direction of the physical value to bedetected and the actual mounting direction of the printed circuit board.

As described above, the present invention provides the followingadvantages.

Since acceleration sensor chips can be produced using a large-diameterwafer, a cost reduction is possible.

In the dicing process for dividing the wafer into respective chipshaving formed thereon sensor part, foreign matter entering the sensorstructure is reduced, thereby achieving a high yield in the productionprocess.

Since a detection principle by a semiconductor strain gauge or amagnetic thin film and a coil is used, if small foreign matter of a sizethat does not disturb the movement of the sensor structure is present inthe gap, the influence on the sensor signal is small.

An acceleration sensor chip with a wide measurement range and a highsensitivity can be achieved.

Since bulk silicon is used for the sensor structure, a highly reliableacceleration sensor chip with repeatability of mechanicalcharacteristics can be achieved.

The present invention can be applied to an angular acceleration sensorchip.

The mounting area of the sensor chip can be reduced, and the entiredetection system including the sensor be down-sized.

As in ordinary ICs, solder-mounting is possible by pins to the printedcircuit board, and the production process of the semiconductor sensorcan be easily automated, thereby reducing the production cost.

Since mounting of the sensor chip to the package is possible byinserting pins into the printed circuit board, direction of the physicalvalue to be detected and direction of the sensor chip can be positivelypositioned in a single direction, thereby improving reliability of thedetection signal.

The present invention has been described in detail with respect topreferred embodiments, and it will now be apparent from the foregoing tothose skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspects, and it isthe intention, therefore, in the appended claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

What is claimed is:
 1. A method of making an acceleration sensor chip comprising: (a) a step for preparing a SOI wafer comprising a silicon substrate, a SiO₂ layer and a silicon thin film; (b) a step for ion implanting a dopant at a position corresponding to a semiconductor strain gauge of said silicon thin film to form a diffusion resistor, and forming devices necessary for circuit construction on said silicon thin film; (c) a step for providing a protective film on the entire surface of said wafer, opening a plurality of through holes penetrating said silicon thin film by patterning and etching, and forming a weight part and a beam part connected to a support frame part on the periphery; (d) a step for removing said SiO₂ layer under said weight part and said beam part by wet etching for forming said plurality of through holes while retaining said protective film; (e) a step for removing said protective film; (f) a step for coating a resist over the entire surface of said wafer; (g) a step for forming a slit by dicing for dividing said chip while retaining a small thickness of said wafer; (h) a step for removing by ashing said resist on said wafer by an O₂ plasma; and (i) a step for dividing said chip by concentrating a stress on said slit.
 2. A method of making an angular acceleration sensor chip comprising: (a) a step for preparing a SOI wafer comprising a silicon substrate, a SiO₂ layer and a silicon thin film; (b) a step for ion implanting a dopant at a position corresponding to a semiconductor strain gauge of said silicon thin film to form a diffusion resistor, forming a magnetic thin film at a position corresponding to a weight part, forming a detection coil surrounding said magnetic thin film, and forming devices necessary for circuit construction on said silicon thin film; (c) a step for providing a protective film on the entire surface of said wafer, opening a plurality of through holes penetrating said silicon thin film by patterning and etching, and forming a beam part connecting to said weight part and a support frame part remained on the periphery; (d) a step for removing said SiO₂ layer under said weight part and said beam part by wet etching for forming said plurality of through holes while retaining said protective film; (e) a step for removing said protective film; (f) a step for coating a resist over the entire surface of said wafer; (g) a step for forming a slit by dicing for dividing said chip while retaining a small thickness of said wafer; (h) a step for removing by ashing said resist on said wafer by an O₂ plasma; and (i) a step for dividing said chip by concentrating a stress on said slit.
 3. The method of claim 1, wherein the dopant is selected from boron and phosphorous.
 4. The method of claim 1, the device necessary for circuit construction comprising at least one device selected from an adjustment circuit, an amplifier circuit, a terminal and wiring.
 5. The method of claim 2, wherein the dopant is selected from boron and phosphorous.
 6. The method of claim 2, the device necessary for circuit construction comprising at least one device selected from an adjustment circuit, an amplifier circuit, a terminal and wiring.
 7. A method of making an acceleration sensor chip comprising: a step for providing SOI wafer comprising a first layer of support substrate, an insulating second layer and a silicon thin film third layer; a step for forming a plurality of cutouts of a same width on said third layer to form a sensor structure having a beam part and a weight part for displacing said beam part which are separated from each other; a step for forming a circuit part connected electrically to said sensor structure in the periphery of said third layer; a step for removing said second layer located beneath said sensor structure to make said beam part and said weight part provided on said sensor structure displaceable.
 8. A method of making an acceleration sensor chip for constructing a sensor structure on a third layer provided on a first layer of support substrate through an insulating second layer, comprising: a first step for forming a plurality of cutouts of a same width on said third layer to form a detection surface of said sensor structure having a beam part and a weight part for displacing said beam part which are separated from each other; a second step for filling said plurality of cutouts of said same width of said sensor structure with a sealing agent to flatten the surface of said third layer including said sensor structure; a third step for forming a circuit part connected electrically to said sensor structure in the periphery of said surface-flattened third layer; and a fourth step for removing said sealing agent filled in said plurality of cutouts of said same width and removing said second layer located beneath a detection surface of said sensor structure to make said beam part and said weight part provided on said detection surface of said sensor structure displaceable.
 9. The method of claim 8, further comprising: a fifth step for coating a protective film on the surface of said third layer including said sensor structure after said fourth step, forming a slit in said protective film-coated third layer, and dicing said sensor chip at said slit, and a sixth step for removing said protective film of said third layer after dicing.
 10. The method of claim 8, wherein in any one of said first step to said fourth step, a film smaller in thermal expansion coefficient than material of said first layer is formed on a backside of said first layer.
 11. The method of claim 8, wherein said same width of said plurality of cutouts formed on said sensor structure is 2 μm or less.
 12. The method of claim 8, wherein said substrate comprising said first layer, said second layer and said third layer, is an SOI (silicon-on-insulator) wafer, or a wafer having polysilicon formed as said third layer on a single crystal silicon substrate through an insulation layer. 